Before you can use cloud resources in a virtual private cloud (VPC), you must create a VPC and a vSwitch. You can create multiple vSwitches to divide a VPC into multiple subnets. By default, the subnets in a VPC can communicate with each other.

VPCs and vSwitches

A VPC is a private network deployed on Alibaba Cloud.

Note You cannot directly deploy cloud resources in a VPC. You must deploy cloud resources in vSwitches of a VPC.
A vSwitch is a basic network device in a VPC and is used to connect cloud resources. You can deploy a VPC only in one region and cannot deploy a VPC across regions. However, a VPC covers all zones of the region to which the VPC belongs. You can create one or more vSwitches in a zone to create one or more subnets for the VPC. VPCs and vSwitches

CIDR blocks and IP addresses

VPCs support both IPv4 and IPv6. By default, VPCs use IPv4. You can enable IPv6 based on your business requirements. For more information, see Create a VPC that supports both IPv4 and IPv6 and Enable an IPv6 CIDR block for a VPC network.

VPCs support the dual-stack mode. In dual-stack mode, resources in a VPC can communicate through both IPv4 and IPv6 addresses. IPv4 and IPv6 addresses are independent of each other. Therefore, you must configure routes and security groups for both IPv4 and IPv6 addresses.

The following table lists the differences between IPv4 and IPv6 addresses.
Item IPv4 VPC IPv6 VPC
IP address format An IPv4 address is 32 bits in length and contains four groups. Each group consists of at most three decimal digits. An IPv6 address is 128 bits in length and contains eight groups. Each group consists of four hexadecimal digits.
Feature status By default, IPv4 is enabled for all VPCs. You can manually enable IPv6.
VPC CIDR block size The subnet mask of a VPC CIDR block can range from /8 to /28. The subnet mask of a VPC CIDR block is /56.
vSwitch CIDR block size The subnet mask of a vSwitch CIDR block can range from /16 to /29. The subnet mask of a vSwitch CIDR block is /64.
Whether you can specify a CIDR block You can specify an IPv4 CIDR block. You cannot specify an IPv6 CIDR block. The system automatically assigns an IPv6 CIDR block to your VPC from the IPv6 address pool.
Supported instance types Supported by all instance types. Not supported by specific instance types.

For more information, see Instance types.

Whether ClassicLink connections are supported ClassicLink connections are supported. ClassicLink connections are not supported.
Whether elastic IP addresses (EIPs) are supported IPv4 EIPs are supported. IPv6 EIPs are not supported.
Whether gateways are supported VPN gateways and NAT gateways are supported. VPN gateways and NAT gateways are not supported.

By default, IPv4 and IPv6 addresses provided for VPCs support only communication over private networks. Cloud resources deployed in different vSwitches that belong to the same VPC can communicate with each other over private networks. To connect a VPC to another VPC or a data center, you can use Smart Access Gateway (SAG), Express Connect, or VPN Gateway. For more information, see Connect a data center to a VPC.

To enable cloud resources in a VPC to communicate with the Internet, configure the following items:

Routes

The system automatically creates a system route table and adds system route entries to control the traffic of the VPC. A VPC has only one system route table. You cannot create or delete a system route table. System route tables
You can create and associate custom route tables with vSwitches to facilitate network management. A vSwitch can be associated with only one route table. For more information, see Work with route tables. Custom route tables

If multiple route entries match the destination IP address, the route entry with the longest subnet mask prevails and is used to determine the next hop. This ensures that the traffic is routed to the most precise destination. You can also add a custom route entry to route traffic to a specified destination. For more information, see Add and delete route entries.